Repelling mosquitoes with new chemicals

By using computational models, chemists created novel and effective repellents …

Mosquitoes are bothersome pests and carriers of parasites and viruses. They are responsible for transmitting diseases to over half a billion people around the world every year, leading to millions of deaths. People commonly use chemical repellents to ward off mosquitoes—DEET (N,N-diethyl-m-toluamide) is still the standard choice, even though it was discovered in 1953. There are other commercial options, but none of them are significantly better at bite prevention, and they don't protect longer than DEET.

As with drug design for the pharmaceutical industry, discovering new chemicals would be too costly if every possible molecule had to be synthesized and tested in the lab. One popular method for overcoming this problem involves using modeling programs to screen for optimized chemical structures before going to synthetic work. Chemists at the University of Florida and the U.S. Department of Agriculture took this approach to produce new mosquito repellents that operate for longer durations than DEET and remain safe for human use.

The scientists built an artificial neural network to predict the structures of new repellents, and provided it with a model constructed from USDA archives that contained repellency information on thousands of chemicals. After screening around 2,000 possibilities, they chose 34 for synthesis. They then tested the effectiveness of these chemicals as topical repellents.

They used a male and female volunteer to test each of the synthesized repellents at two different concentrations (2.5 or 25 μmol per cm2 of cloth spread area). At the higher concentration, compound A effectively warded off mosquitoes for 73 days, while DEET protected for 17.5 days. With the lower concentration, compound B kept mosquitoes at bay for 13.5 days; DEET was effective for only 2.5 days.

Thus, the scientists were able to use an artificial model to successfully discover new candidates for pest repelling. As long as the new repellents are safe for use in the long run and can be commercialized at a reasonable price, we can look forward to experiencing better protection from those pesky mosquitoes.

Yun Xie / Yun Xie / Yun Xie is a contributing science writer at Ars, where she covers the latest advancements in science and technology for Ars. She currently works in scientific communications, policy, and review.